The invention relates generally to lamps, and more particularly to a field emission lamp.
Lamps are virtual necessities in modern daily living, and a conventional luminescent lamp generally adopts mercury vapor. In use, electrons are accelerated by an electric field so that the accelerated electrons collide with the mercury vapor. This causes excitation of the mercury vapor and subsequent remission. The remission process causes radiation of ultraviolet rays. The ultraviolet rays irradiate a fluorescent material of the lamp, whereby the ultraviolet rays are converted into visible light.
However, the mercury vapor is toxic to humans and environmentally unsafe. Therefore in recent years, field emission lamps which adopt carbon nanotubes as emitters have been manufactured to replace conventional luminescent lamps.
Referring to FIG. 2, a field emission lamp as disclosed in an article entitled “A Full Sealed Luminescent Tube Based on Carbon Nanotube Field Emission” and authored by Mirko Croci. et al (page 329-336, Vol. 35, Microelectronics Journal 2004) is shown. The field emission lamp 20 includes: a glass tube 21 open at two ends thereof, and having a plurality of feedthroughs 211, 212, 213, 214 formed therealong; a conductive layer 22 formed on an inner surface of the glass tube 21; a phosphor layer 23 formed on the conductive layer 22; a first endpiece 27 and a second endpiece 28 mated with the open ends of the glass tube 21 respectively; a cathode fixing pole 241 located at the first endpiece 27; a cathode down-lead pole 242 located at the second endpiece 28; and a cathode 24 fixed between the cathode fixing pole 241 and the cathode down-lead pole 242. The cathode 24 has a carbon nanotube layer (not shown) formed on a surface thereof. Furthermore, a spring 243 is fixed between the cathode 24 and the cathode down-lead pole 242, a conductive annular ring 25 is formed on the inner surface of the glass tube 20 at opposite ends of the conductive layer 22 and the phosphor layer 23, a plurality of getters 29 are located at the first endpiece 27 and connected with the feedthroughs 211, 213, and a pumping stem 26 is located at the second endpiece 28. The conductive annular ring 25 is electrically connected with an anode (not shown) via the feedthroughs 212, 214. The pumping stem 26 is sealed after evacuation of the field emission lamp 20, and the getters 29 are used to absorb residual gas in the glass tube 21.
In use, the anode is grounded, and an appropriate negative voltage is applied to the cathode down-lead pole 242, thereby forming a strong field along the surface of the cathode 24. The strong field excites the carbon nanotubes on the surface of the cathode 24 to emit electrons, and the electrons bombard the phosphor layer 23 on the inner surface of the glass tube 20, thereby producing visible light.
The field emission lamp 20 does not use mercury vapor, and is safe for humans and environmentally friendly. Furthermore, the field emission lamp 20 adopts a cold cathode, thereby providing a high electrical energy utilization ratio and low energy consumption. However, the field emission lamp 20 has the two ends that need to be encapsulated, and each encapsulation procedure is complicated and time-consuming. This means that the field emission lamp has a relatively high cost.
What is needed, therefore, is a field emission lamp having a simple structure and low cost.